Re: [Xen-users] pvgrub2(-like?) booting methods for PVHv2 guests

[Hans van Kranenburg <hans@xxxxxxxxxxx>]

On 01/23/2018 06:41 AM, Juergen Gross wrote:
> On 23/01/18 05:46, Andy Smith wrote:
>> Hi,
>>
>> What are the current options for booting PVHv2 guests in Xen 4.10.0?
>>
>> As far as I can see there is only direct kernel booting, i.e.
>> supplying "kernel = /path/to/vmlinux".
>>
>> In PV land there is pvgrub which is very convenient for being able
>> to use kernel and initramfs, but I am not seeing support for that in
>> upstream grub2. I see that Juergen Gross post a patch series that
>> claims to add this feature:
>>
>>     <https://lists.gnu.org/archive/html/grub-devel/2017-11/msg00054.html>
>>
>> …but this doesn't seem to have been applied yet. Is it an ongoing
>> idea or has that method been abandoned?
> 
> Still waiting for review.

Since I wanted to try to test this, I scraped the patches off the
grub-devel list and did the following:

1. clone https://git.savannah.gnu.org/git/grub.git
2. apply patches on top of master, plus an extra one with a puzzle piece
to make it actually compile (see attachment)

3. build:
./autogen.sh
./configure --target=i386 --with-platform=xenpvh
make

4. use mkstandalone to create a grub image to boot
./grub-mkstandalone -d grub-core --locale-directory=/ -o
~/grub-i386-xenpvh-fire-ze-missile -O i386-xenpvh
~/build/pvgrub2/pvgrub2/xvda-fire-ze-missile.cfg

contents of the config file that I want to have inserted into it (same
file I use for booting PV now):

root='(xen/xvda)'
insmod xzio
insmod gzio
insmod btrfs
insmod ext2
echo 'Loading Linux ...'
linux /vmlinuz root=/dev/xvda ro elevator=noop
echo 'Loading initial ramdisk ...'
initrd /initrd.img
boot

5. Try to use it already, to see what happens. (Xen 4.10.0)

-# cat yolo-pvgrub2

type="pvh"
kernel = "/yolo/grub-i386-xenpvh-fire-ze-missile"
name = "yolo-pvgrub2"
memory = 1024
vcpus = 10
vif = [
    "mac=02:00:0a:8c:d9:0d,bridge=ovs0.217",
]
disk = [
    '/dev/test/yolo,raw,xvda,rw',
]

-# xen create -c yolo-pvgrub2
Parsing config from yolo-pvgrub2
libxl: info: libxl_create.c:109:libxl__domain_build_info_setdefault:
qemu-xen is unavailable, using qemu-xen-traditional instead: No such
file or directory
S3 disabled
S4 disabled
CONV disabled

                     GNU GRUB  version 2.03

   Minimal BASH-like line editing is supported. For the first word, TAB
   lists possible command completions. Anywhere else TAB lists possible
   device or file completions.


grub>

Ok, so for some reason it seems to ignore the config? But I can type
things manually:

grub> insmod xzio
grub> insmod gzio
grub> insmod btrfs
grub> insmod ext2
grub> search.file /vmlinuz
 xen/xvda

Ok, so it can see the disk and fine the symlink to the kernel image. Now
let's try the rest of it:

grub> root='(xen/xvda)'
grub> linux /vmlinuz root=/dev/xvda ro elevator=noop
grub> initrd /initrd.img
grub> boot

And now it just hangs, no output any more.

6. Apply linux patches to the domU kernel and Xen

domU Linux kernel:
- Branch off from linux 4.14.14
- add https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git as
remote and cherry-pick the 4 patches mentioned in
  https://lists.gnu.org/archive/html/grub-devel/2017-12/msg00017.html

Xen: pick this one on top of 4.10.0:
 https://lists.xen.org/archives/html/xen-devel/2017-11/msg01807.html
 4a5733771e6f33918eba07b584cccce564a67ac1

7. Test again after dom0 reboot into the new xen and put the new domU
kernel on it.
 -> same result: grub command prompt, and no activity after 'boot'.

Extra things:

8. Start domU after copying kernel/initrd to the dom0:

type="pvh"
kernel = "/yolo/vmlinuz-4.14.14-yolo"
ramdisk = "/yolo/initrd.img-4.14.14-yolo"
root = "/dev/xvda ro elevator=noop console=hvc0"

This boots, dmesg: http://paste.debian.net/plainh/7120cef2

9. Just for fun, start domU with previous kernel/initrd without the patches:

type="pvh"
kernel = "/yolo/vmlinuz-4.14.0-3-amd64"
ramdisk = "/yolo/initrd.img-4.14.0-3-amd64"
root = "/dev/xvda ro elevator=noop console=hvc0"

This boots and has 1 vcpu and no ACPI lines in dmesg, which is expected
breakage, I believe, reading xen-devel.

So, what am I missing?

Hans

Attachment: grub-pvh.tgz
Description: application/gtar-compressed

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